Reaching any of the parking lots often requires 4WD - there are two lots on Tunnel Rd and another on Shafer Run.  The warming hut is not accessible by car, it's at the bottom of a valley.  There's a flat trail leading there from the Shafer Run parking lot - see the trail map. 
To get to Shafer Run, take 31 to Bakersville.  Do not attempt to use Tunnel Rd to get to Shafer Run in winter!  

North Woods trail map

Laurel Highlands Nordic Ski Patrol patrols this area at weekends.

Winter recreation guide from Forbes State Forest
Forbes State Forest trail map
Forbes State Forest map collection